In such display systems, the pictures are defined on a viewing screen by an assembly of dots projected thereon by an electron beam whose intensity is controlled by a luminance signal of variable level. With television-type screen scanning for example, the location of a dot is given by an address P(i,j) in which i represents the order of a scanning line and j the position of the considered dot in that line. Associated with each impage point P(i,j) is a luminance signal of level S(i,j) normally specifying the brightness of a dot of given dimensions known in the art by the term "pixel".
The pictures obtained in this type of display system are subject to certain defects due to the existence of spurious phenomena interfering with the luminance signals. Known techniques permit the elimination of certain image defects if the latter are identified without ambiguity, that is to say in practice if their level is invariable and known. This is for example the case with mono-ionic or ionizing-particle noise in an image-intensifying-tube circuit and with interferences producing a black or a white dot in a vidicon tube. These techniques utilize the prior knowledge of the shape of the curve of the luminance histogram of the picture, the curve showing along the ordinate the number of dots of a given brightness level. The conventional way of interference suppression consists in replacing the luminance signal of any dot whose level is equal to or higher than the level of the interfering signal by a signal of the most probable level of the picture. This process is the more effective the narrower the histogram, i.e. the smaller the typical deviation of the number of dots along the curve from a peak representing the most probable brightness level. Still, there are drawbacks in particular if the interferences to be eliminated are in a range of very improbable levels. These dots consequently carry a great amount of information, in the statistical sense of the term, and their suppression results in a loss of overall information. This loss of information can only be evaluated with knowledge of the subjective degree of interest shown by the observer for the information conveyed by the image points subjected to this leveling procedure. Thus, if the level of the luminance signal of the spot to be eliminated is in the domain of brightness of the particular details looked for in the picture by the observer, the elimination of these levels by the aformentioned process in fact renders the corrected picture irrelevant.